The present invention relates to an improved tubing hanger and running tool which overcomes the disadvantages of the prior subsea hanger running tools.
Running tools are typically designed to support the weight of a tubing hanger and its associated tubing string during tubing installation on a subsea well completion. In prior devices which are hydraulically operated, difficulties are encountered through a loss of the hydraulic system. This is particularly true since the hydrostatic fluid pressure is very substantial in subsea environments and can exert very substantial pressures on the exposed piston surfaces of the running tool. Some prior running tools were provided with a separate umbilical to ensure that the desired hydraulic pressure could be maintained to avoid the pressure responsive latching means from responding to the substantial hydrostatic pressures encountered at the subsea location. Since it is desired to maintain the running tool in latched engagement with the hanger after the hanger is landed until downhole work is completed, the release of the running tool from the hanger should be possible even when hydraulic latch pressure is lost prior to release. Some prior tools have solved this problem by closing a blowout preventer on the running tool string and then applying pressure through the choke or kill line of the BOP stack. This pressure surrounds the running tool and will cause the latch actuating sleeve of the running tool to retract to its unlatched position allowing retrieval of the running tool.
It is also possible with prior devices that as a result of needing to maintain the hydraulic latch pressure to resist the action of the hydrostatic pressure, the loss of the hydraulic latch pressure during the running of the tubing can result in the unlatching of the running tool. A further disadvantage of those prior tools which have separate umbilicals to the surface is that the umbilical control line is at risk during the lowering from the surface.
U.S. Pat. No. 3,693,714 discloses a tubing hanger with a running tool which uses pressure of hydraulic fluid delivered through the running string and relies on either a locking dart to direct the hydraulic pressure to urge the locking sleeve in the locked direction and an unlocking dart to direct the hydraulic pressure to urge the locking sleeve in the unlocked direction.
U.S. Pat. No. 4,262,748 discloses a hanger and running tool which is secured to the hanger by spring loaded segments and releasing ring on the hanger which on full seating of the hanger cams the segments out of engagement with the hanger to release the running tool therefrom.
U.S. Pat. No. 4,067,388 discloses a running tool and a casing hanger with a split latch ring having external threads which are engaged within the internal hanger threads and a piston ring which wedges the split latch ring into latching engagement with the hanger. Release is either by retraction of the piston ring or by rotation to thread the latch ring out of engagement with the hanger.
U.S. Pat. No. 4,712,621 discloses a casing hanger running tool which is moved between running, setting, releasing and dumping positions. Also, there is a hydraulic system to control a piston which moves latching dogs supporting the hanger on the running tool. Hydraulic fluid is delivered through the bore of the tool.
U.S. Pat. No. 4,736,799 discloses a running tool which is operated by hydraulic fluid delivered through control passages to lower, land, set seal and release from the hanger. A spool valve is provided in the hydraulic system to allow for failure in the release line.